Question 6.5: Comparing Electron Affinities of Different Elements Why does...
Comparing Electron Affinities of Different Elements
Why does nitrogen have a less favorable (more positive) E_{ea} than its neighbors on either side, C and O?
The magnitude of an element’s E_{ea} depends on the element’s valence-shell electron configuration. The electron configurations of C, N, and O are
Carbon: 1s^{2} 2s^{2} 2p^{1}_{x} 2p^{1}_{y} Nitrogen: 1s^{2} 2s^{2} 2p^{1}_{x} 2p^{1}_{y} 2p^{1}_{z}
Oxygen:1s^{2} 2s^{2} 2p^{2}_{x} 2p^{1}_{y} 2p^{1}_{z}
Carbon has only two electrons in its 2p subshell and can readily accept another in its vacant 2p_{z} orbital. Nitrogen, however, has a half-filled 2p subshell, so the additional electron must pair up in a 2p orbital where it feels a repulsion from the electron already present. Thus, the E_{ea} of nitrogen is less favorable than that of carbon. Oxygen also must add an electron to an orbital that already has one electron, but the additional stabilizing effect of increased Z_{eff} across the periodic table counteracts the effect of electron repulsion, resulting in a more favorable E_{ea} for O than for N.